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Rheem Prestige 9.9GMP with Intermittent DHW

gotgas
gotgas Member Posts: 85
in THE MAIN WALL

We built a new house with a Rheem Prestige 9.9 GMP Combi-Boiler. The model is RCBH199DVLP. We are having trouble with intermittent domestic hot water.

The DHW stopped entirely two weeks ago. It would flow, but would not heat. The DHW side never fired. The heat side continued to fire with no problems.

This was diagnosed (I think correctly) as a faulty three-way valve. The way these are set up (as I understand it) is the DHW will take preference when the unit detects flow and shut down the heat side.

Since the valve was been replaced, DHW is returned. It works fine sometimes, but sometimes will only run cold. We are going to get the techs back out Monday, but I was thinking on this problem and thought I might have an idea.

Is it possible when they were working with the unit they changed the setting that makes the DHW higher priority? I am speculating that the DHW is not firing while the heat is firing. Is that a possibility with these units?

Any help is appreciated. Our new homeowners are very gracious, but they bought a new house and would like it to work. Thank you!

Comments

  • neilc
    neilc Member Posts: 2,973

    do you have pictures?

    is there any zone controllers? are they set correct?

    zone valves or circs? let's see pictures, wide angle, showing everything, floor to ceiling

    known to beat dead horses
  • hot_rod
    hot_rod Member Posts: 24,321

    it is triggered by a flow switch, maybe .35 to .50 gpm. Somewhere near the switch or in the unit is a small strainer, look in your manual for location. As they plug it prevents the unit from getting adequate flow to trigger. It is an easy thing to check and it may need periodic service.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    bjohnhy
  • bjohnhy
    bjohnhy Member Posts: 96

    Post photos of DHW piping into and out of combi, and recirculation pipes.

    Any pattern to when it runs cold?

    Any error codes?

    What is temperature of the incoming cold?

    The boiler heating component is working well?

    I second to make sure filter is clean.

    This symptom is sometimes caused by crossover between hot and cold pipes somewhere else in the house. Shower valves or unchecked recirculation lines are some potential sources.

    Larry Weingarten
  • gotgas
    gotgas Member Posts: 85

    Sorry about the slow reply. Helping to cater a wedding. Here are the boiler pictures:

    20240201_084207.jpg
  • gotgas
    gotgas Member Posts: 85
    20240201_084211.jpg
  • gotgas
    gotgas Member Posts: 85
    20240201_084217.jpg
  • gotgas
    gotgas Member Posts: 85
    20240201_084222.jpg
  • gotgas
    gotgas Member Posts: 85
    https://forum.heatinghelp.com/discussion/comment/1841420#Comment_1841420

    No error codes. I have not discerned a pattern. Incoming temp is approx 54F year round. Boiler heat side is fine, no problems. I will check the filter. We piped the whole house so I am pretty sure there is no crossover.

    Thank you!

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